history-db, now speeding up 'bzr log'

[John Arbash Meinel]

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>> There is still some polishing and edge-case work to do. However, I think
>> it has at least shown what I hoped to show.
> 
> In terms of polish, I think we need to get things to the point where a
> single configuration settings controls whether the cache is used or not.
> In other words, I'd like to see the 'create-history-db' step disappear
> and become implicit.

create-history-db is optional at the moment, but currently the cache is
only updated when a tip changes. We certainly could have a check for "if
not tip in db: Importer(tip)".

Doing just 'bzr up' will put the same data in the db that
create-history-db does, it will just take a little bit longer as it
'create-history-db' is tuned for doing the whole history, and
post-branch-tip-changed is tuned for doing incremental updates.



> 
> Sorry if you've explained this already but what's the plan from here wrt
> storage technology: stick with a generic db or move to custom files?
> 
> Ian C.
> 

For stuff like Loggerhead and Launchpad, using an SQL backend seems
perfectly reasonable. For core tech, I'm not very happy about it.

John
=:->

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